Messages in this thread | | | Date | Tue, 11 Sep 2001 08:48:24 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: linux-2.4.10-pre5 |
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On Tue, 11 Sep 2001, Daniel Phillips wrote: > > But see my post in this thread where I created a simple test to show that, > even when we pre-read *all* the inodes in a directory, there is no great > performance win.
Note that I suspect that because the inode tree _is_ fairly dense, you don't actually need to do much read-ahead in most cases. Simply because you automatically do read-ahead _always_: when somebody reads a 128-byte inode, you (whether you like it or not) always "read-ahead" the 31 inodes around it on a 4kB filesystem.
So we _already_ do read-ahead by a "factor of 31". Whether we can improve that or not by increasing it to 63 inodes, who knows?
I actually think that the "start read-ahead for inode blocks when you do readdir" might be a bigger win, because that would be a _new_ kind of read-ahead that we haven't done before, and might improve performance for things like "ls -l" in the cold-cache situation..
(Although again, because the inode is relatively small to the IO cache size, it's probably fairly _hard_ to get a fully cold-cache inode case. So I'm not sure even that kind of read-ahead would actually make any difference at all).
Linus
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